The present invention relates to a method of bonding a plastic clip such as a retainer onto a natural fiber based porous member such as an automobile door trim by welding, and a plastic clip for use in the bonding method.
As a door trim or the like of an automobile, for weight reduction and cost saving, natural fiber based porous members including epoxy plastic as a binder are often utilized. Since the door trim or the like contains as much as 70% in weight of natural fiber, stamping is used for its forming. Therefore, the plastic clip such as the retainer for attaching the door trim to the automobile body is formed separately from the door trim which is made of the natural fiber based porous member. Therefore, the plastic clip such as the retainer is required to be integrally connected with the natural fiber based porous member of the door trim. To this end, ultrasonic welding or the like has been used. For example, Japanese Patent Laid-open No. 04-208656 discloses a method of attaching a fastener of a plastic clip to a roof lining having a glass fiber substrate by ultrasonic welding. In accordance with that attaching method, a portion of the attaching side of the plastic clip is melted into the glass fiber portions and voids thereof, so that a tangled bond of plastic and the glass fibers can be obtained. To apply it to a case where the plastic clip is bonded onto the natural fiber based porous member by welding, this attaching method must be somewhat improved.
As described above, in the automobile door trim, the natural fiber based porous member including epoxy plastic as a binder is often used. When the epoxy plastic clip is ultrasonic-welded onto the natural fiber based porous member, including epoxy plastic as a binder, its bond strength often is not stabilized. Therefore, in order to obtain higher bond strength than a certain level, very high ultrasonic energy and very large pressure force are required for welding. As a result, the deformations due to heat affections and the pressed dents of the ultrasonic welding tip may appear on the bonding side and the rear side of the clip. Thus, it is desired to provide a method that can bond the clip with low energy, without any heat affections and any dents to the rear side of the clip when the plastic clip is bonded onto the natural fiber based porous member.
Japanese Patent Laid-Open No. 03-67722 discloses a method of ultrasonic-welding a plastic retainer clip onto a door trim. In this patent, the problems of the heat affection and dent are pointed out, and a proposal is made to eliminate the boundary gap between the door trim and the retainer bracket. In particular, a projected ridge is formed on the attaching side of the retainer bracket, the projected ridge is positioned in a recess of the attaching side of the door trim and then melted for bonding by ultrasonic-welding to fill the gap between the recess on the attaching side of the door trim and the outer side of the retainer bracket. In this method, there is a restriction in molding of the door trim because a recess for receiving the retainer bracket is necessary on the attaching side of the door trim. Therefore, it is desired to bond the plastic clip onto the natural fiber based member, without such restriction, any heat affections and any dents to the rear side, and also with lower energy.
Other technologies for welding another plastic part onto a plastic member are described in Japanese Patent Laid-Open No. 63-212532, Japanese Patent Laid-Open No. 63-278821, and Japanese U. M. Laid-Open No. 02-124131. In Japanese Patent Laid-Open No. 63-212532, the projected leg is formed on the attaching side of the plastic bracket and is ultrasonic-welded so that the plastic brackets are bonded onto the plastic roof lining of the automobile. However, this welding has excessive molten portions of the legs. Also, in Japanese Patent Laid-Open No. 63-278821, a plastic retainer for holding a small accessory is welded onto a plastic product so as to attach the small accessory on the plastic product. For the purpose of welding the retainer, a projection is provided having sharp tip end on the bonding side of the retainer. This projection is then melted to bond the retainer onto the plastic product. Again, there is excessive molten portions of the projections. In Japanese U. M. Laid-Open No. 02-124131, a projected portion is formed as a welding site in a core material portion of the wooden fiber based mat so as to ultrasonic-weld the plastic part onto the wooden fiber based mat. A welding portion of the plastic part is positioned on the projected portion for ultrasonic-welding. The melted welding portion of the plastic part preferably tends to be penetrated into the core material of the wooden fiber based mat, however, it is difficult to form the projected portion as the site for welding in the core portion of the wooden fiber based mat.
Therefore, an object of the present invention is to provide a method of bonding a plastic clip and a plastic clip for use in the bonding method, wherein when the plastic clip is bonded onto the porous member, there is no restriction on the shape of the natural fiber based porous member, wherein the clip can be bonded with low energy, without any heat affections and any dents on rear side of the clip, and wherein the excessive molten portions will be easy to handle.
To accomplish such object, according to the present invention, there is provided a method of bonding a plastic clip onto a natural fiber based porous member by welding. The method comprises steps of; forming a plurality of projections in a welding region of the bonding side of the plastic clip to extend to the natural fiber based porous member and a plurality of recesses adjacent the projection in the welding region for receiving the excessive molten portions of the melted projections, and further a reference level portion in a region other than the welding region at the bonding side of the plastic clip to define the welding height of the plastic clip; positioning the bonding side of the plastic clip at a predetermined position of the natural fiber based porous member; and fusing the bonding side to weld and bond the plastic clip onto the porous member.
According to the present invention, there is also provided a plastic clip for use in the above plastic clip bonding method. The plastic clip comprises a welding region and a non-welding region, the welding region is formed with a plurality of fusible projections extending to the natural fiber based porous member and a plurality of recesses adjacent the projections for receiving the excessive molten portions of the projections, and the non-welding portion is formed with a reference level portion to define the welding height of the plastic clip.
In the plastic clip, the projections and recesses may be alternately formed with each of the projections and recesses being aligned in a line. The clip may also be made of material having a high grade of melt flow index (M.F.I.). This insures that the molten plastic material can easily impregnate into voids of the natural fibers, thus high energy is unnecessary, and both the bonding strength and the peeling resistance are increased.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood, however, that the detailed description and specific examplesxe2x80x94while indicating preferred embodiments of the inventionxe2x80x94are intended for purposes of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.